Achieving Low Contact Resistance to Aluminum with Selective Tungsten Deposition

The inability of physical deposition methods to deposit metals in small diameter openings in integrated circuits is a limiting factor in the development of integrated circuits with reduced dimensions. Recent results have shown that selective deposition of tungsten using an experimental low pressure chemical vapor deposition (LPCVD) process is capable of completely filling such openings resulting in high yields of low contact resistance connection between a molybdenum metallization layer and a second metal layer of aluminum. Previous reports indicated that tungsten deposited selectively on a first level of aluminum gave contact resistances two orders of magnitude higher. In this report the authors describe a process capable of depositing selective tungsten on aluminum with low contact resistance. This has been accomplished with the single wafer, experimental system used previously and also with a multiwafer, production system. The data indicate that higher deposition rate and/or higher wafer temperature during tungsten deposition are important in achieving low contact resistance.